Open a command prompt on the server giving you this issue. Run: vssadmin list writers. Any writers not stable and running are in error. A server restart normally fixes this. Do that, try running the job again, and post back with an update.

I am assuming, this happens immediately after a power outage. Perform the steps mentioned by Craig. When the power outage happened were there any backups running. If so, you need to see ifg there are any orphaned snapshots or shadowcoppies present. Have you found any errors in the Event Viewer regarding VSS or shadow copy or snapshot errors.

Do you have any hardware VSS provider installed. See if this document help